The present invention relates generally to semiconductor fabrication and more particularly to the design of a wafer etch system having simplified diffuser element removal. By simplifying diffuser element removal, operating efficiency can be enhanced.
Known wafer etching systems such as the GCA Wafer Etch System 606/616 manufactured by the GCA Corporation of Sunnyvale, Calif. or the Drytek Triode Wafer Etch System available from Drytek/Triode, a unit of General Signal, Inc. typically include a diffuser element in the form of a plate. The diffuser plate provides uniform distribution of, for example, a gas which is to be formed into a plasma discharge for etching a semiconductor wafer placed into the system. The semiconducter wafer is usually located between an upper electrode assembly and a lower electrode assembly of the etch system, with the diffuser plate being mounted in the upper electrode assembly.
A diffuser plate available with the upper electrode assembly of the aforementioned GCA or Drytek etch systems is shown in FIG. 1. As shown in FIG. 1, the diffuser plate 2 is formed as a unitary structure which includes a circular mounting portion 4 having four mounting holes 6 for receiving mounting bolts (not shown). The circular mounting portion encompasses an interior diffuser portion 8 having a number of diffusing holes 10 arranged about a center point of the diffuser plate.
A partial cross sectional schematic of an upper electrode assembly similar to that of the GCA or Drytek triode etch systems is shown in FIG. 2. As can be seen in FIG. 2, an upper electrode assembly 11 includes a tunnel portion 12 which encases a gas feed 13. The upper electrode assembly includes an electrically isolated upper electrode shown generally as element 15, which is placed at an RF potential and which is O-ring sealed into place by mounting the tunnel 12 onto an upper electrode housing 23. A cylindrically shaped upper chamber 21 supports the upper electrode housing 23 which includes a ground grid assembly 16 mounted to the housing 23 in known fashion.
More specifically, the upper electrode housing includes a flange 19 which forms a support for mounting the ground grid assembly. A clamping ring assembly 25 used for holding down the edge of a wafer(s) and for forming a sealed plasma zone is also mounted to the upper electrode housing 23. The ground grid assembly 16 (representing a middle electrode) is thus mounted directly beneath the upper electrode assembly and is placed at ground potential. The ground grid assembly is ceramically isolated from the upper electrode assembly in known fashion.
A ceramic insulator 18 is formed as part of the upper electrode assembly to support the upper electrode 15. When properly placed in the upper electrode assembly, the ceramic insulator 18 provides adequate space between the upper electrode housing 23 and the upper electrode 15 for supporting the diffuser plate 20, such as that described with respect to FIG. 1. The diffuser plate 20 is situated in a sealed, dark space area of the upper electrode assembly and is attached to the upper electrode so as to be placed at the RF potential of the upper electrode.
The diffuser plate 20 is mounted by inserting mounting bolts through holes in the diffuser plate and into threaded mounting holes 22 of the upper electrode 15. Because the threaded mounting holes 22 are formed in the upper electrode, and because the diffuser plate is mounted above the flange 19, the diffuser plate must be mounted to the upper electrode 15 before the upper electrode assembly 11 is assembled.
A lower electrode assembly 24 is further provided with a lower electrode at an RF potential. A plasma zone is formed in the interior of the upper electrode housing 23 between the ground grid assembly 16 and the electrode of the lower electrode assembly 24 via a hydraulic closing of the upper electrode assembly in a direction indicated by arrow 26. Upon closing of the upper electrode assembly, a wafer(s) placed near the lower electrode assembly is encompassed within the plasma zone whereby etching of the wafer(s) can be performed. The vaccum chamber is pumped during etching to a low vacuum state via a vacuum means 17 to draw gas from the upper electrode assembly into an area near the ground grid assembly area.
The aforedescribed wafer etch system thus uses a mounting system which permits an operator to access the diffuser plate and upper electrode assembly for regular cleaning and maintenance of the components. Such cleaning and regular maintenance of the diffuser plate and upper electrode assembly is necessary in order to remove particle build-up (e.g., polymers and residual gas build-up) on these parts due to high temperatures in the etching system. If ignored, the particle build-up can inhibit proper, accurate etching of wafers.
Any effort to access the diffuser plate requires the operator to dismantle the upper electrode assembly. However, dismantling of the upper electrode assembly involves significant time which results in significant maintenance and operating costs. In addition, the increased time over which the upper electrode assembly is dismantled during regular cleaning renders the etching system susceptible to contamination (e.g., due to particles, moisture) which cannot easily be removed and which can seriously impede proper operation of the etching system.
More specifically, because a number of mounting bolts and vacuum sealing rings are associated with the upper electrode assembly to provide an uncontaminated vacuum, great amounts of care and time must be expended to ensure proper reassembly of the upper electrode assembly following maintenance. However, the fear of prolonged upper electrode assembly exposure to the atmosphere significantly inhibits such precise reassembly and can result in human error during reassembly. Further, because the diffuser plate must be cleaned relatively frequently (e.g., preferably every 250 etched wafers, but at a minimum of every 500-1000 etched wafers), the entire upper electrode assembly is dismantled an excessive number of times (e.g., the upper electrode assembly is preferably dismantled for cleaning every 1500 etched wafers) such that the risk of improper reassembly due to errors is enhanced substantially.
While the lower side of the diffuser plate included in the aforedescribed etch systems can be cleaned from below without removal from the upper electrode system, several problems are associated with this technique. For example, cleaning the lower side of the diffuser plate with D.I. water placed upon a lint free cloth results in the migration of moisture through the diffuser plate and into the upper electrode assembly, thus inhibiting proper operation of the etch system. Further, prolonged exposure of the diffuser plate during cleaning enables particles and moisture to migrate into the upper electrode assembly.
Another technique is to leave the diffuser plate in place over a longer period of time by reducing the frequency with which preventative maintenance cleaning is performed. However, failure to regularly clean the diffuser plate can result in the production of wafers having a relatively high defect rate. For example, particulate formed by the plasma reactions in known etch systems can attach to all interior, exposed surfaces of the etching system. After sufficient build-up, the particulate may flake off onto a semiconductor wafer being etched and contaminate the wafer, thus reducing yields of properly fabricated wafers.
Accordingly, it would be desirable to provide a wafer etch system which does not incur the maintenance time and associated operating costs generally associated with semiconductor fabrication.